I'm not sure if this has already been posted before, I have looked using the search but no matching results.
When waiting for the shops to re-stock items which takes 2 days, the process can be very slow and tedious :S watching that little marker count down the hours.
To make life easier try this:
Set the wait time (usually 24 hrs) then press A to begin countdown and immedietly press your Xbox Guide button and you will hear the tick sounds in the background rapidly counting doen at about 3 per second instead of the usual 1 every 1.5 second. I know this isnt a huge improvement but when you waiting for that special something to appear in the shops, the amount of time you save waiting is huge!!
Try it and hope it helps.
-Just to confirm, this takes the total wait time (real time) from 56 seconds down to 12 seconds when passing a total of 48 hours game time-